In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
One component of wireless communications networks where it may be challenging to obtain good performance and capacity is the antennas of network nodes configured for wireless communications; either to/from another network node, and/or to/from a wireless user terminal.
For example, massive beam forming, i.e., beam forming using active antenna arrays with orders of magnitudes more antenna elements than used in current communications networks, is expected to become a technical component in the radio access part of future fifth generation (5G) communications networks. By using large antenna arrays at the radio base stations, user data can be transmitted focused in space so that energy is received mainly by the wireless device dedicated by the user data, thus resulting in little interference being perceived by other wireless devices or other types of nodes. Massive beam forming has therefore the potential to increase system capacity and energy efficiency by orders of magnitudes.
One potential issue with massive beam forming may be related to the fact that the beams may be so narrow that data may only be received by the dedicated wireless device. For user data this is desired, but some data, e.g., system information, preferably needs to be transmitted to all, or at least most of, wireless devices (i.e., broadcasted) in the communications network.
Therefore such data should be transmitted with wide coverage in order to reach all wireless devices. Some ways to address this issue will be summarized next. However, as also noted, each of these ways have their drawbacks.
According to a first approach, a separate wide-beam antenna may be used for transmission of broadcast data. A drawback with this approach is that it requires additional hardware.
According to a second approach, broadcast data is transmitted using a single antenna array element, or sub-array, of the antenna. This array element or sub-array will have a wider beam than the full array of the antenna. A drawback of this approach is that only one, or a few, power amplifiers (PAs) in the antenna array is/are utilized, which thus wastes power resources.
According to a third approach, amplitude and/or phase tapering is used over the full array of the antenna to widen the beam. Drawbacks with such tapering are that amplitude tapering gives poor utilization of the PA resource and that it is in many cases not possible to synthesize the desired beam shape using phase-only tapering.
According to a fourth approach, broadcast data is transmitted sequentially in different directions using narrow beams. A potential drawback with this approach is that this takes longer time and consumes more resource elements than transmitting broadcast data simultaneously in all directions with a wide beam.
Other scenarios where it may be desired to use wide beams with an antenna array with many elements is in millimeter-wave (mmW) communications, which is an access technology foreseen to be a part of 5G radio access. Due to the increased propagation loss at such high frequencies, high gain beam forming may be needed to retain the link budget, possibly both at the receiver and transmitter. Beam forming may be needed since the dominant propagation paths between a transmitter and a receiver are typically not known a priori. Testing all combinations of a large number of narrow transmit and receive beams in order to find the best beam pair may consume a prohibitive amount of time/frequency resources. A way to resolve this issue may be for the radio base station to start the search procedure with wide beams and then make the beams narrower and narrower until the best pair of narrow beams has been found. Such a beam finding procedure generally requires means for generating beams with different beam widths in a flexible manner. In order to fully utilize the antenna array and the available PA resource it may be desired to use all antenna elements and all PAs at full power when transmitting beams with different beam widths.
Hence, there is a need for improved beam forming.